A cooling air passage structure of an alternating-current generator (AC generator) for a vehicle is known (refer to JP 2008-43041, for example). In such a structure, an intake of cooling air flow from a rear side of an engine is avoided in order to improve a coolability of semiconductor elements installed, while securing a quantity of the cooling air flow by suppressing an increase of a fluid loss.
In the AC generator for the vehicle described above, a second rear cover is attached to a back of a first rear cover, and an air intake duct is attached to a side of the second rear cover. The cooling air flow is taken in the second rear cover through the air intake duct.
By the way, in the cooling air passage structure disclosed in JP2008-43041, since the cooling air flow introduced through the air intake duct flows in from the side of the second rear cover, the cooling air flow is taken into the first rear cover from a vicinity of an exit of the air intake duct.
Therefore, the cooling air flow hardly reaches a rectifier arranged in an area far from the exit of the air intake duct, thus arises a problem with an insufficient cooling efficiency.
Moreover, since the first rear cover and the second rear cover are provided, the flow of the cooling air flow taken into the second rear cover is once stopped by the first rear cover, thus arises another problem that the amount of the cooling air decreased because of a growth of ventilation resistance.
Further, the second rear cover attached to the back of the first rear cover has a fixing surface arranged to a position larger than an exterior of a frame excluding p part of a stay.
Therefore the frame requires a part that projects to the exterior side that corresponds to the fixing surface that results a size of an outline to grow partially, and installing manner is deteriorated.
Furthermore, besides the first rear cover equipped in the general AC generator for the vehicle, the second rear cover is needed so that a number of parts increases, and, therefore, there is a problem that an assembly man-hour and a part cost increase.